Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

166
FXUS63 KLOT 140829
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
329 AM CDT Tue Apr 14 2026

.KEY MESSAGES...

- Late spring to summer-like temperatures will continue through
  Friday with highs in the 70s and 80s and lows in the 60s.

- Several additional rounds of showers and thunderstorms,
  including a threat for severe weather and flooding expected,
  especially late this afternoon/evening and again on Wednesday.

- A brief break in the pattern is expected late Thursday into or
  through the day on Friday before another storm system arrives
  in the Friday evening to Saturday timeframe.

- In the wake of the Saturday cold front, a brief, potentially
  sharp, shot of much cooler air could bring frost/freeze
  concerns into next Sunday and Monday.

&&

.DISCUSSION...
Issued at 328 AM CDT Tue Apr 14 2026

Today through Wednesday Night:

A weakening MCS will continue drifting across northern Illinois
through this morning in a weakening phase with a gusty outflow
boundary surging out ahead of it. The OFB passage may bring a
temporary period of onshore winds and notably cooler conditions
to portions of the lakeshore (especially far NE IL) and perhaps
patchy fog as well. Towards and after sunrise this morning, a
question will be the extent to which widely scattered elevated
convection (showers and isolated non-severe storms) may develop
with southward extent behind the outflow boundary. Once any
convection this morning fades out, expect the rest of the
morning and into the early afternoon to be dry as the area once
again becomes capped underneath a strong EML (elevated mixed
layer) inversion.

A likely key player the rest of this afternoon for the looming PM
severe threat will be how far south the outflow boundary from the
weakening MCS reaches, before retreating back north as an effective
warm front. A farther south remnant outflow boundary could conceivably
aid in a bit farther south convective initiation (CI) near the
stalled warm front this afternoon than depicted verbatim by most
of the CAM guidance. On the other hand, low clouds shifting
southward in the wake of the OFB this morning will serve to limit
insolation initially, potentially delaying stronger destabilization
until the mid afternoon. Conceptually, the area to monitor for
explosive CI this afternoon will in closer proximity to the
stalled warm front (as previously noted), from northwest Illinois
and northeast Iowa into southern Wisconsin. Satellite, observational,
and mesoanalysis trends will need to monitored closely for any
subtle 700 mb impulses that could help erode the cap as early as
3-5pm. A secondary possible area to watch for isolated storms by
the mid to late afternoon will be into portions of central IL as a
500 mb vort lobe translates east-northeast.

Ultimately, the lack of stronger large scale forcing (neutral h5
height tendencies) casts some uncertainty/conditionality to this
setup. An ensemble of recent CAM solutions does suggest a
realistic play for the daylight hours remaining dry across our
CWA counties. With the OFB placement wildcard and possibility
that subtle upstream impulses can sufficiently erode the cap,
we maintained (30-50%) chance PoPs as early as 3-5 PM over the
northwest 1/3 to 1/2 of the CWA, and stair-stepping gradually
south from there.

Once clouds scatter enough early this afternoon, several hours of
diurnal heating and destabilization of the moist (dew points in
the 60s) low-level air mass topped by very steep lapse rates aloft
will yield a very favorable thermodynamic environment for severe
storms (MLCAPE possibly at or bit upward of 3k J/kg). In the
presence of about 40 kt of deep layer bulk shear, this will be a
conditionally volatile environment for supercells capable of very
large hail (2"+). If CI occurs into the CWA prior to sunset, somewhat
weaker low-level flow and storm relative inflow (especially if
sfc winds remain veered) would indeed favor damaging to
potentially destructive hail as a primary threat initially.
As the low-level jet diurnally intensifies into this evening, a
notable tornado threat could also unfold into northeast IA,
southern WI, and possibly far northern IL, given enlarged low-
level hodographs. Any locally backed surface winds would further
enhance SRH.

With the above being said, despite the 3/5 severe threat level
(enhanced risk) for locations north of I-80 today-tonight
(Tuesday-Tuesday night), our confidence is a bit lower in
storms effectively tapping into the volatile environment today
within our CWA. A later after sunset arrival into far northern
Illinois and mid-late evening farther south would give some
time for instability to wane. Also, the relatively parallel
alignment of the deep layer shear vector to the warm front
should lead to a storm mode transition from supercells to
upscale growth into forward propagating segments through the
evening. Mismatched west-southwesterly 850-300 mb flow vs.
propagation vectors towards the east-southeast may limit how far
south and east an appreciable damaging wind (and embedded QLCS
type tornado threat can reach). All in all, the area of greatest
concern for potential significant severe weather is well
outlined by the zone of 10% tornado probs in SPC`s day 1
outlook, approximately near and north of a Dixon to Highland
Park IL line.

Additional storms should eventually fill in behind the evening
activity overnight, favoring our highest official PoPs of the
night into the 60-70% range. Hydrology may become an increased
concern later tonight, particularly if repeated rounds of storms
move over the same area. If this occurs, a notable threat of flash
flooding will materialize, perhaps more than implied by a flood
threat level of 1/4 (marginal risk) in WPC`s excessive rainfall
outlook. Exactly how the event will play out through tonight
remains quite uncertain.

With so much riding on the effects of prior convection into
Wednesday morning, little can be gleaned about Wednesday PM`s
threat for strong to severe storms with any sort of confidence. It
looks quite messy/muddled and we won`t be able to sort things out
until more is known about the environmental evolution. A 2/5
threat level (slight risk) remains targeted for areas northwest of
I-55 in SPC`s initial day 2 outlook, with a level 1/5 (marginal
risk) I-55 and southeast, including Chicago. At present,
independent of where any corridors of severe storms set up, likely
veered surface winds, modest low-level flow just off the deck,
and mid-level lapse rates not quite as steep, seem to point
towards damaging winds as the primary threat after any initial
hail threat. Mesoscale evolution may yield a localized enhanced
tornado threat, as per the outlook discussion.

Castro/KJB

Thursday through Monday:

There`s variance regarding the progression of a cold front
across the region, with some of the slower solutions holding
onto some potential for storms into Thursday afternoon
(particularly southeast ~1/2 of CWA). Thereafter, into Thursday
night and at least the start of Friday, ensemble model guidance
advertises a brief break in the stormy pattern as shortwave
ridging moves through the Great Lakes ahead of a substantial
trough digging into the central US. High temperatures look to
rebound into the low to even mid 80s by Friday accompanied by
another potential threat for strong to severe thunderstorms
Friday night into Saturday. Thereafter, there is a reasonably
strong signal in ensemble guidance for a cooldown to start next
week.

The key aspect for the weekend into early next week cooldown is
a recent trend towards a much cooler air mass due to trough
amplification over the region. If this comes to pass, parts of
the area may flirt with sub-freezing temperatures Saturday night
into early Sunday, and again Sunday night into next Monday
morning. With the summer-like warmth and rain this week
supercharging plant growth and leaf out, the magnitude of the
weekend cold shot will be one to watch for agricultural interests.

Castro/Borchardt

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1249 AM CDT Tue Apr 14 2026

Key messages for the 06Z TAF period:

* Gusty southwest winds and LLWS overnight.

* A period of gusty SHRA and embedded TS early this morning.

* Winds may shift to north-northeast behind an outflow boundary
  with the SHRA/TS, SE/ESE for a time this morning, before
  returning to southwesterly.

* MVFR CIGs after sunrise until early afternoon.

* Additional TSRA expected Tuesday late afternoon into night.
  Low confidence on exact timing and coverage.

A weakening line of showers and embedded thunderstorms should
move across the TAF sites early this morning until just after
sunrise. Main window of opportunity is 08 to 12Z at RFD and 09
to 13Z in Chicago. If the convection doesn`t weaken too much,
heavy rainfall and vsby reductions down to MVFR may occur.
An southward shifting outflow boundary near the northern MKE
suburbs as of this writing may get an assist to surge south as
severe storms to the west intersect it. Concern here is for a
period of onshore winds (possibly gusty at initially) at the
Chicago terminals before returning to southwest by mid morning.

MVFR CIGs will likely settle overhead during or just after the
rain and persist through the morning Tuesday. Guidance has
trended later in the day with a return to VFR with early
afternoon now favored.

Additional thunderstorms are expected over the airspace later
Tuesday, as early as late afternoon with higher chances during
the evening and night. Confidence is low on the exact timing and
coverage of storms at the terminals, and PROB30s in the latest
TAFs correspond to the windows of seemingly greatest potential.
However, storms are a possibility anytime after mid-afternoon
through the overnight. Severe weather will be possible if TS
impact any terminals in the late afternoon-early evening.

SW winds will regularly gust between 25 and 30 kt through the
pre-dawn hours today, along with LLWS due to ~60 kt winds at
about 2kft AGL. Expect SW winds gusting between 20 and 25 kt
during the day on Tuesday. Direction could get squirrelly in
the vicinity of storms both early this morning (as noted
earlier) and again this evening through the overnight.

Doom/Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 7 AM CDT this morning for the IL
     and IN nearshore waters.

&&

$$

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